Instead of plug/mold for roof?

[kapnD]

I’m thinking the OP was suggesting using aluminum foil as a bond breaker between the foam mold and layup.

 

[waikikin]

Greetings to all,

Instead of using a mold/plug to create a hard-top roof for my boat, why can't I just use foam material and design the roof the way I want, cover it with aluminum foil and then plaster on top of it all?
Possible or not?
Downsides doing this method?

Most success is had with pre finished sheets/melamine etc, back before that available we used to use masonite, shellac and johnsons floor wax, corner fillets can be done with poly filler plus wax and pva.
Jeff.

 

[Geno67]

Dodger build for a sailboat, foam and fiberglass.

Wow. What kind of foam is that? He called it PVC. That is amazing 90 kilos to break a piece that weighs 360 grams and spans half a meter with one layer of glass on either side. I bet you could build a hardtop I could walk on with a couple of layers on each side.

 

[wet feet]

Wow. What kind of foam is that? He called it PVC. That is amazing 90 kilos to break a piece that weighs 360 grams and spans half a meter with one layer of glass on either side. I bet you could build a hardtop I could walk on with a couple of layers on each side.

He called it PVC because that is what it is,the best type of foam for general marine use but not the cheapest foam available.There are many different brands and here are a couple of examples; Structural Core Materials https://www.gurit.com/structural-core-materials/
Divinycell - PVC foam core materials from Diab https://www.diabgroup.com/products-services/divinycell-pvc/.

The earlier suggestion to use sheets of melamine faced material to build a mould is the way I would approach the job as it greatly reduces the time needed to get a good finish.I'd expect the corners to need a little attention though.

 

[kitcarman]

That dodger - and the videos are first - class. What a great result. Got me wondering whether honeycomb (nidaplast or similar) would get a better or worse strength or be lighter? Possibly not much in it, but does anyone have experience of PVC vs honeycomb?